Traditionally, aircraft have been given forward motion by engines in pods located either below or in wing structures or tail rudders. These engine pods have generally incorporated a turbine engine which draws air from its inlet through the engine to provide an outlet flow accelerated by combustion to provide propulsion. It will be appreciated that such propulsion is relatively noisy and the engine pods take the form of cowlings which add to drag. The engine itself will also add significantly to weight and with only a limited number of engines failure of one engine greatly reduce the propulsive power available.
Ideally, the means of propulsion should have as limited an effect on drag and as low a weight contribution as possible whilst being configured to utilize fuel as efficiently as possible. Furthermore, the engines used for propulsion should be easily maintained.
Previously, it has been suggested to provide large numbers of lift fans associated with a turbine engine (see GB847,868) for vertical take-off. However, these fans generally direct air flows from a source engine rather than their own propulsive contribution. Furthermore, there is no consideration of energy recovery and efficiency.